The invention relates to a method for monitoring yarn run/stop conditions.
According to a method as known from DE-A4 417 222 (U.S. Pat. No. 5,477,892) the working sensitivity level of each of a group of weft yarn feelers is adjusted by inputting the yarn quality into a selector device having pre-set sensitivity level adjustments associated to different yarn qualities. Any set working sensitivity level is used unchanged during operation of the weaving machine. Although yarn quality is decisive for the working sensitivity level adjustment a predetermined and unchangeable adjustment of the sensitivity level has to be a compromise and does not consider further parameters also of influence for the needed working sensitivity level. For example, for a given yarn quality (yarn number) the response behaviour of an electronic weft yarn feeler varies depending from the surface quality, material flexibility and roughness of the yarn, the linear specific mass of the yarn, yarn tension and yarn speed, and moreover varies due to other parameter variations arising during weaving from the weaving behaviour or special design of the weaving machine. Such parameters are e.g. yarn tension variations, braking variations, yarn oiling, temperature, humidity, etc. A predetermined working sensitivity level strictly associated to the yarn quality precautionary has to consider all said parameters with their worst possible influence and thus is far too high. An unnecessarily high working sensitivity level, however, leads to missing stop signals because the best sensitivity level adjustment is the lowest sensitivity level that can avoid false stop signals.
Furthermore, it is known from practice on some rapier weaving machines to provide a possibility on the main control panel to select and vary different working sensitivity levels or amplification factors for the piezo-electric weft yarn feelers. Each working sensitivity level can be adjusted by the operator. However, this needs advanced skill and attention by the operator but only can lead to a working sensitivity level adjustment which for safety reasons has to be higher than actually needed.
It is a task of the invention to provide a method of the kind as disclosed allowing to reliably operate the weaving machine with an optimum working sensitivity level for each weft yarn feeler without the necessity to carry out remote adjustments.
Each respective weft yarn feeler is automatically and continuously adjusted to an optimum working sensitivity level for the respective weft yarn. Due to the automatic adjustments of the working sensitivity level not only the yarn quality but all other effectively occurring and varying parameters are considered continuously. According to the method the effectively used working sensitivity level is oscillating about an optimum adjustment level in the most decisive moments of an insertion cycle. This means that the sensitive level is permanently adjusted to the summary of all influencing parameters such that it fits to the instantaneous conditions and will follow any developments for better or worse. This eliminates false stop signals and avoids stops of the weaving machine only caused by a too low sensitivity level.
According to the invention the periodic procedures of the weft insertion is taken care of by carrying out adjustments on the basis of sampling the detected run output signals synchronised with said periods. It can be convenient to monitor the run output signal and to control the amplifier""s gain individually for the feeler by multiplexing the signals and by assigning a time slot for each channel. Alternatively, it is even safer to observe the run output signal of the weft yarn feeler in two different time slots and by using two different sensitivity levels, namely the higher working sensitivity level used to confirm the run/stop conditions and the lower observation sensitivity level to observe if said lowered sensitivity level could lead to a stop.
According to the invention the lower observation sensitivity level is used to investigate safely if the lowered sensitivity level would not generate a false stop. If it turns out at the lower observation sensitivity level that the observed run output signal is stable this is taken as the confirmation that both sensitivity levels now can be lowered without the danger of a false stop. This is continued until the output run signal starts to become unstable at the observation sensitivity level. This then is taken as a proof sign to not further lower both sensitivity levels, but to now raise both sensitivity levels for a predetermined amount in order to stay on the safe side. Since the adjustment method is carried out continuously the effectively used working sensitivity level will oscillate around an optimum sensitivity level for the weft yarn in question and with consideration of all further influencing parameters.
Advantageously the difference between the present working and the observation sensitivity level is maintained essentially constant and just big enough to avoid undesirable machine stops.
In order to avoid extreme sensitivity level adjustment behaviour, it is advantageous to lower both sensitivity levels only after a predetermined number of consecutive insertion cycles have occurred with the run output signal at the lower observation sensitivity level maintaining stable. Only after having registered said number of consecutive insertions cycles with stable output signal behaviour both sensitivity levels commonly are lowered by a certain amount.
Advantageously both sensitivity levels are raised, also by a predetermined amount only, in case that an observation confirms an instability of the run output signal. In combination this means that lowering both sensitivity levels only is only carried out after first confirming a predetermined number of correct insertion cycles, but both sensitivity levels immediately are raised in case of occurring signal instability. As long as the run output signal at the lower observation sensitivity level remains stable both sensitivity levels are lowered step by step in order to approach an optimum working sensitivity level as soon as possible.
Both sensitivity levels may either be raised and lowered always by one step or for a predetermined time interval.
In order to maintain the effectively used working sensitivity level close to an optimum sensitivity level it is expedient to have only one step difference between the working sensitivity level and the observation sensitivity level.
In order to achieve a high resolution of the adjustment it is preferred to use about 32 steps. Each step represents an individual signal amplification factor meaning that the adjustments carried out actually is a step-wise variation of the amplification factor.
According to a preferred embodiment of the method the run output signal within the restricted observation interval of each insertion cycle is sampled in different adjacent time slots for both sensitivity levels. Said method can easily be carried out with a microprocessor or microcontroller using the same circuitry for the observation as is used for gaining the working signal output. This means that the microprocessor of the weft yarn feeler is consecutively switching back and forth between both sensitivity levels without the danger of losing any significant run output signal variations.
Preferably the observation interval is restricted to an angle range of a full revolution of the rapier weaving machine beginning at about 220xc2x0 to 280xc2x0 and ending at about 280xc2x0 to 310xc2x0. This means that the observation is carried out within essentially the angle range used to evaluate the correct run/stop conditions as well. Within said angle range in a rapier machine relatively smooth speed and tension variations are occurring in the yarn, which is advantageous for the reliability of the method.
In case that a weft yarn feeler device consisting of several weft yarn feelers is used, either each individual weft yarn feeler is controlled individually or the result of the observation of one of the weft yarn feelers is used to also adjust the working sensitivity level of other weft feelers processing an equal yarn or the same yarn quality.